This invention relates to a transit providing a lead-through for electric cables or pipes that are required to extend through an opening in a wall, bulkhead, partition or the like. This invention concerns certain improvements in a particular kind of transit as hereinafter defined and which is for use with cables, wires, pipes or tubes or the like elongate elements commonly used in an installation for conducting electricity, service commodities such as gas, oil or water, or enclosing such service lines. For convenience herein, the term "cable" is used and should be interpreted in the context to include all such aforesaid elongate elements.
This invention is particularly concerned with a transit of the kind now defined as comprising a rectangular metal frame defining an opening through which the cables are to extend, a series of sets of modular blocks for assembly in rows within the frame opening, the blocks being adapted for surrounding each cable or for blanking off a modular space, and a compression and packer assembly for mounting in the frame opening to clamp the assembled blocks together and around each cable with the compression and packer assembly completing filling of the frame opening.
Such defined kind of transit for cables is well known and is disclosed in patent specification GB No. 1,049,621.
Typically, transits of the defined kind are used in a wide range of applications and are installed in various environments including hazardous and have to meet specific regulations for fire-proof or flame-proof or gas-tight installations. Usually, a transit has to be assembled on site and often the working conditions at the installation site are difficult in many respects, such as: access and location; the numbers, types and sizes of cable; limited working space and lack of access to both inlet and exit sides of the lead-through; and, ambient temperature, weather and environmental conditions.
Conventionally in transits of the defined kind, in each series set of the modular blocks, each block is of square section and has a length substantially the same as the depth of the metal frame into which the blocks are assembled in an array of superimposed rows. Each block in a set of blocks has the same external dimensions and a plurality of blocks from one set will completely fill one row across the inside of the frame. To provide blanks at locations in a row where no lead-through is required, each set includes solid blank blocks for assembly in the row. For a cable lead-through, the blocks have a through hole of a diameter corresponding to the diameter of the cable to be surrounded by the block, and to facilitate fitting and assembly each such block is formed in two complementary halves with semi-cylindrical recesses that, when aligned, provide the lead-through hole in which the cable is seated.
This invention as later described may be applied to transits for use with such modular blocks as just mentioned or with other forms of modular blocks used for the same purpose of providing the lead-throughs for the cables or pipes and blanking blocks for filling the modular space where no lead-through is required.
This invention is particularly concerned with the compression and packer assembly of a transit of the defined kind.
As will be understood, the compression and packer assembly is arranged to be received within the frame to fill the remaining space left after the rows of modular blocks defining the lead-throughs and blanks have been assembled. The compression and packer assembly has to apply pressure to the assembled array of modular blocks and cables to clamp these together and around the cables whilst also completely filling the frame. It is important in practice that such compression and packer assembly be simple to install and in many applications it is essential that the correct pressure is applied to the assembled array either to avoid excessive clamping forces being applied to cables which must not be stressed or deformed, for instance optic cables, or to avoid insufficient clamping forces which could lead to failure in sealing required and or ineffectual retention of the arrayed modular blocks within the frame so that the transit assembly fails to provide a complete barrier in a wall, bulkhead or the like as intended.
In the common known transits of the kind defined, the compression and packer assembly relies on the resilient deformation of a packer block or blocks which are inserted in the frame to fill the remainder of the opening after the modular blocks and cable have been assembled. Due to the inherent properties of the assembled modular blocks and cables, before the packer can be inserted, the assembled array has to be forced down into the frame to provide a clearance opening into which the packer can be inserted. Commonly, this initial compression is achieved by using a pressure plate which seats on the final row of modular blocks and a load is applied to the plate by a bolt which is mounted in an end wall of the frame and which can be unscrewed to engage the pressure plate and then on further unscrewing gradually applies the load to the assembled array of modular blocks to force them together around the cables.
Once this stage has been completed, then a packer block corresponding to the internal width of the frame and designed to seat on the plate engaging the inner faces of the side walls of the frame has to be inserted into the clearance space with the packer having a cut-out or suitable recess for the bolt which has to be left in situ maintaining the compression on the assembled array of blocks and cables whilst the packer block is so inserted. The packer block is then expanded by a squeezing action applied between front and rear faces of the packer block by a clamping arrangement, and then the forces applied to the assembly enclosed within the frame are distributed with all of the parts and the cables being subject to compression loads to maintain the desired clamping and sealing engagement. The bolt is left in situ although it is usually no longer needed to apply any compression to the array of blocks and cables as the pressure is now applied through the expanded packer block engaging the pressure plate. The cut-out or recess in the packer block may be filled by a packer piece which is either fitted onto the bolt initially or which is finally inserted when the last adjustment of the bolt is completed.
This arrangement leads to many complications on site as the main single packer block has to be entered into the clearance space from one side of the frame whilst manipulation of the bolt and any insertion of the packer piece is from the other side. In addition due to the effect of the assembled modular blocks and cables, often it is impossible to ensure that excessive and damaging pressure is not applied to the cables and modular blocks.
To overcome such disadvantages, other proposals have been made and some implemented in use by providing a combined and adjustable compression and packer assembly which can be inserted into the clearance space when in a contracted condition, and then expanded in a direction within the plane of the frame and transverse to the axes of the cables so as to apply the desired pressure to clamp the assembled modular blocks, cables and packer together tightly within the frame opening. However, even with such adjustable compression and packer assembly difficulties in practical use arise due to the need to squeeze the packer assembly into the clearance space whilst attempting to hold the arrayed modular blocks and cables in situ, and in addition, problems also arise from the uncontrolled nature of the expansion of the compression and packer assembly and the forces generated within the frame during fitting.
It is an object of this invention to provide an improved transit of the kind defined for cables or pipes which has a particular form of compression and packer assembly which is both simple and easy to use in assembly of a transit as well as obviating known disadvantages with existing transits systems such as referred to previously.
It is a further object of this invention to provide a compression and packer assembly which provides versatility for fitting and installation requirements.
Other objectives and advantageous features of this invention will be referred to later herein with particular reference to exemplary embodiments of this invention.